Abstract :
Gamma-ray bursts (GRBs) are among the most powerful explosions in the Universe, marking the catastrophic death of a massive star (long-duration GRBs) or the merger of a compact binary involving a neutron star (short-duration GRBs). Regardless of the progenitor, a spinning, stellar-mass black hole or a highly magnetised neutron star will eventually be produced. After accreting material, these central engines will launch two relativistic jets that interact with the medium surrounding the burst through external shocks, producing the so-called afterglow via synchrotron emission. Therefore, GRBs serve as unique laboratories for studying physical processes under extreme conditions. Due to their unique ability to trace the late-time evolution, radio observations, along with X-rays and optical, have proven to be a fundamental tool to contrain the geometrical (opening angle, viewing angle and angular structure of the jet) and physical (energy retained by the relativistic electrons and the magnetic field, profile of the surrounding medium, electron distribution index,...) parameters that govern the dynamics of GRBs.
Moreover, the high angular resolution provided by very long baseline interferometry (VLBI) is essential for measuring the apparent superluminal expansion (in on-axis GRBs) and proper motion (in off-axis GRBs) of the GRB blast wave, offering a crucial insight into the structure and dynamics of GRB jets, complementary to light curve and spectral modelling. This presentation will highlight the significant contribution of radio observations to GRB science, with a particular focus on recent results concerning GRB221009A, the brightest GRB recorded to date. For this event, the observed size evolution probed by VLBI measurements suggests that the reverse shock and the forward shock dominate the afterglow emission at different frequencies and times. Lastly, future prospects for GRB research through radio interferometry will be discussed.
